Bright silver plating



Patented Jan. 19, 1954 BRIGHT SILVER PLATING Otto Kardos, Keyport, N.J., assignor to Hanson- Van Winkle-Munning Company,

Matawan,

N. J., a corporation of New Jersey No Drawing. Application September 15,1950, Serial No. 185,171

' This invention relates; to silver plating and more particularly to theelectrod'eposition' of bright silver depositsfrom silver cyanide platingbaths.

I have discovered that reactionproducts of ketones, especially ofacetone, methyl ethyl ketone and acetonylaoetone "(2,5-hexanedione).with carbon disulfide and alkali hydroxide, when properly purified, areexcellent brighteners for cyanide silver solutions. v 1 i 'Ihave furtherdiscovered that these ketonecarbon disulfide reaction products cooperatevery strongly with small amounts of Turkey red oil @(sulfonated castoroil), if the concentration of the latter is maintained within rathernarrow limits.

Various sulfur-containing compounds such as: carbon disulfide, ammoniumthiosulfate, potassium ethyl xanthogenate, thiourea, alkalidithiocarbamates, mercaptobenzothiazole, mercaptothiazole andmercaptothiazoline have been'proposed and used as silver brighteners.Also the simultaneous use of Turkey red oil with potassium xanthogenateand of Turkey red oil with carbon disulfide as addition agents has beenproposed.

' 'A' thorough examination of these addition agents, as well as manyother sulfur-containing compounds such as: beta -Mercaptoethanol, 2-inercaptoethyl pyridine, ethylene thiourea, dithiobiuret, rhodanine (2-thiono-4-keto-thiazo1idine), 2,4-diketothiazolidine, thioammeline,dithioammelide, ZA-diamino-6 thio-1,3,5-thiadiazine and various alkalisoluble ammonium thiocyanate-formaldehyde resins, showed that theaddition of the above agents, alone or with Turkey red oil, did not giveas brilliant a silver deposit as the deposit from a silver plating bathcontaining the ketone-carbon disulfide reaction products. Theketone-carbon disulfide reaction products in a silver plating bath alsopermitted the use of a wider currentdensity range and the bath was morestable.

The reaction of ketones of the general type RCH2COCH2R and carbondisulfide in the presence of powdered potassium hydroxide has beendescribed by Apitzsch, Ber. 37, 1,599 (1904) 38, 2,888 (1905) and41,4028 (1908).

I'have extended this reaction to the gamma diketone acetonylacetone(2,5-hexanedione), and have found that the reaction proceeds also inpresence of a 50% solution of aqueous sodium hydroxide; slowly foracetone and methyl ethyl ketone, rapidly for acetonylacetone. I havealso found that these reaction products are able to react withformaldehyde.

'10 Claims. (01. 204-46) For the application as silver brighteners, itis very important that the sodium sulfide (or hydro'sulfide) formed bythis reaction is completely eliminated from the ketone-carbon disulfidereaction products before their addition to the silver plating bath. Thisis done by acidulating the end product of this reaction withmineralacid, whereby. the ketone-carbon disulfide reaction product precipitatesand hydrogen sulfide is formed. The precipitate is then thoroughlywashed with water, redissolved'indilute aqueous sodium hydroxide andreprecipitated with acid. This purification of the reaction product bydis: solution in dilute aqueous sodium hydroxide and precipitation withmineral acid can be repeated several times. The final product can bedried in vacuo and powdered. Weaker acids, such as acetic acid, do notprecipitate these reaction products. However, after boiling away thehydrogen sulfide, such solutions can also be used as silver brighteners.

A preferred formula for an aqueous silver bath is:

oz./gal. Silver cyanide 8.0 Potassium cyanide 18.0 Potassiumcarbonate r6.0 Potassium hydroxide 0.4

But obviously this is but one example of many possible bath. formulas-When, to such a bath, 0.02 to 0.04 oz./gal. -of a methyl ethylketonecarbon disulfide reaction product, or of an aceto-,nylacetone-carbon disulfide reaction product, were added together with10 ml./l. of Turkey red oil (50%), excellent silver electrodeposits wereobtained in the Hull cell over a wide current density range. But afterabout one day's standing oruse of the bath, the degree of brightness ofthe electrodeposits is considerably reduced and the current densityrange of brightness considerably narrowed and it isv not possible torestore the excellent initial bath performance by addition ofketone-carbon disulfide reaction product. Turkey red oil or other bathcomponents. It has been found that ifonly 0.8 m1./l. of Turkey red oil(50%) is used, together with 0.02 to 0.04 oz./gal. of ketone-carbon.disulfide reaction product, there occurs, on standing of the bath, firstan improvement of the bath performance, fol: lowed by a slow decrease ofthe brilliancy ofvthe silver deposit; but the brightness range is notnarrowed. In this case, that is whenonly 0.8 m1./l. of Turkey red oil(50%) have been added, the initial excellent bath performance can beeasily restored by the addition of small amounts of the ketone-carbondisulfide reaction product, approximately 0.01 oz./ gal. per week ofstanding. Addition of only 0.4 ml./l. of Turkey red oil (50%) to asilver bath containing 0.02 to 0.04 oz./gal. of ketone-carbon disulfidereaction product, initially produces matte and streaky silver deposits.An improvement is noticed if the bath has been standing for severalhours. The presence of 1.6 ml./l. of Turkey red oil (50%) will, uponstanding, gradually narrow the brightening range of the electrodeposits.The limits for the concentration of Turkey red oil, for continuoussatisfactory bath performance, are between; 0.4 'rnL/l; and 1.6 ml./l.or preferablyddmk/lj. to 1.2 rnl-./1. of Turkey red oil (50%).

It should be recorded that some of the methyl ethyl ketone-carbondisulfide' reaction products produced excellent silver electrodepositsover'a wide current density range, even in absence. of.

Example 1 22.8 g. (0.2 mol)v acetonylacetone 6,1 g. (0.8 mol) carbon.disulfide 96g. (1.2 mols) aqueous sodium hydroxide solution (50%) wereput into a. 'c1'os ed bottle or flask supplied with reflux condenser.

' On occasional shaking, the. two-phase reaction mixture darkened, amoderate heat evolution occurred. and after about 45 minutes the mixturewas homogeneous, dark red-brown and fairly warm. The mixture was then"cojole'dto room temperature and diluted with 400 ml. oi Water. 1.2.mols of hydrochloric acid (1:1 by volume) were then slowly added understirring. An almost black resinous ma'ss'w'a's precipitated and muchhydrogen sulfide escaped. The precipitate was powdered, washed withwater and redissolved with 0.8 mol of aqueous sodium hydroxide. Thissolution was then diluted toapproximately 500ml and 0.8-mol ofhydrochloric. acid (1:1 by volume) were added under stirring. The darkbrown precipitate was filtered off, washed with water and airor vacuumdried. 0.02 'ozz/gal. of this reaction product, when added to the silverbath as described above, gave a semibright silver deposit in the Hullcell up to about: 20 amps/sq. ft. On addition of 0.8 ml./l'. (0.1 fl.oz./gal.-) of Turkey redoil (50%), a brilliant silver deposit wasobtained in the Hull cell up to 20 amps/sq. it. On agitation ina beaker,brilliant silver deposits were obtained up to '45 amps/sq. ft.

Addition of only 0.4 ml./'l-. 'of- Turkey red oil (50%) gave at first-amatte irregular silver electrodeposit, and onlyafter several hoursstanding could fair deposits be obtained. With 1.6- ml./l. of Turkey redoil, the bath showed some deterioration of performance-on standing, andcould not be restored to its initial good performance.

1 .In a more dilute bath prepared from 70 'oz./'gal. Silver cyanide 6.0.Potassiumcyanide -11 1.4.0 Potassium, carbonate g g i 4.5,- Potassiumhydroxide -1 A oz./gal. Acetonylacetone-carbon disulfide reactionproduct 0.02 Turkey red oil'(50%) 0.1 fl. oz./gal.

bright silver deposits up to amp/sq. it. could be obtained only withstrong mechanical agita tion of the bath.

For the preparation of small amounts of acetonyl-acetone-carbondisulfide-alkali hydroxide reaction product, temperature control is notrequired as the reaction is moderately fast and exothermic andthe uppertemperature range is limited by the boiling point of carbon disulfide.For the preparation of larger amounts of reaction product, strongcooling of the reaction mixture. is required after an initial inductionperiod of about to 60 minutes, so that the reaction does not. become tooviolent. For highest yields or solid reaction product, final maintenanceof the reaction mixture at C. for several hours, before precipitationwith acid, is useful.

Example 2 0.2 mol acetonylacetone 0.8 mol carbon disulfide 1.2 molsaqueous sodium hydroxide. solution reacted as in Example 1.

- Then, after dilution to 600 ml, instead of hydrochloric acid, slightlyover 1.2 mols of acetic acid-were added. The solution. was boiled downto 400 ml neutralized with potassium hydroxide solution, diluted to 600ml. and filtered. 8 ml. of, this dark red brightener solution, whenadded to 1 liter silver bath, produced bright silver electrodeposits upto about 20 amps/sq. ft. in the Hull cell, the brightness of which wasfurther increased by addition, of 0.8: mL/l. Turkey red oil (50%).

On standing, the brightener stock solution deteriorates slowly,apparently by formation of sodium sulfide but can be restored to itsinitial performance: by acidulation with acetic acid, boiling andneutralization.

Example 3 0.2 mol acetonylacetone 0.8 mol carbon disulfide 1.2 molsaqueous sodium hydroxide solution reacted 'as-i'n Example 1'.

After the. mixture. had become homogeneous, it was cooled, to roomtemperature and 0.1 mol. (7.5 ml.) of aqueous. formaldehyde (37%) Wasadded. Anv exothermic reaction occurred, and after about 15. minutes thereaction mass was cooled, diluted andprecipitated as. in Example 1. Ablack resinous lump. precipitated, was Washed. with water and hardenedon standing overnight. It was powdered, dissolved in aqueous. sodiumhydroxide, precipitated with. dilute hydrochloric acid. (1:1 by volume).in an amount at least equivalent to, the. sodium hydroxide used,filtered, Washed, redissolvedin aqueous sodium hydroxide andreprecipitated. with hydrochloric acid. After air drying, 19.5 grams ofa. light brown powder were obtained. The results obtained with this.addition agent in a. silver bath werethe same as. those obtained withthe additionagent'des'cribed iii-Example 1. Similarlyeffective-addition. agents were obtained by using 1.6 instead of 1.2.mols-of sodium hydroxide, or using 0.2.mo1' of.formaldehydeinsteadof0.1mo1; m 0

, Example 4 14.4 g. (0.2 mol) methyl ethyl ketone 30.5 g. (0.4 mol)carbon disulfide 48.0 g. (0.6 mol) aqueous sodium hydroxide solution(50%) The above was shaken occasionally in a closed bottle for about twoweeks, after which time the mixture became homogeneous. Then .7.5' ml.(0.1 mol) of formaldehyde (37%) were added and, after standing forabout15 minutes, an addition of 300 m1. of water and finally 0.6 mol ofglacial acetic acid were made. The solution was heated to drive out allhydrogen sulfide; and after addition of 0.6 mol. of sodium hydroxide itwas diluted to 400 ml. 4 ml. of this brightener solu-, tion, when addedto 1 liter of silverbath, ploduced brightsilver electrodeposits over awide current density range. Their brightness was further increased byaddition of 0.8 ml./l. of Turkey red oil (50%). p r r Example 5 25 g.(0.35 mol) methyl ethyl ketone 100g. (1.31 mol) carbon disulfide 751g.(1.33 mol) potassium hydroxide (powdered) 1 ml. water tated, which wasdissolved in 20 ml. of sodium hydroxide solution (20%), reacted with 15ml. of

formaldehyde (37 precipitated with dilute hydrochloric acid and, afterfiltering, redissolved in sodiumhydroxide and precipitated again withhydrochloric acid. A brown powder resulted which, after washing withwater and air drying, was used as'an addition agent to' the standardsilver bath. 0.04 oz./gal. of this product produced brilliant silverdeposits in the Hull cell and in a'beaker at up to 30 amps./sq.'ft. withagitation. Similar brighteners were prepared without the use offormaldehyde. In general, the presence of formaldehyde willfacilitatethe formation of the final products in powder form andincrease the yield of these reactions.

Example 6 10.5 g. (0.145 mo1) methyl ethyl ketone 19 g. (0.25 mol)carbon disulfide t 22 g. (0.39 mol) potassium hydroxide (powder),

and

7.5,to 25 g. dimethoxytetraglycol The 'above were reacted in a flaskunder reflux.

The presence of dimethoxytetraglycol accelerated the reactionconsiderably. After about 15 minutes, the brown reaction product wasdissolved in. 200 ml. of water. This solution wasthenacidulated with 25ml. of glacial acetic Other :batches-='gave brilliant silver depositsonly inpresence of small amounts of Turkey red on: Also the presence ofTurkey red oil increases the tarnish resistance of: the silverelectrodeposits. Here again, with .10. ml./l. of Turkey red oil (50%),the deposits were excellent in the beginning, but'the'current densityrange over which brightness could be obtained narrowed consider.- ablyafter afew hours standing of the bath, and the initial wide brightnessrange could not be restored by any. additions. Withonly 0.8 ml./l. ofTurkey red oil (50%) the bath performance .remained fairly stableandcould be completely re-e stored by small periodic additions ofketonee carbon disulfi'de brightener.

Similar addition agents were obtained from acetone instead of methylethyl ketone.

The carbon disulfide reaction products of diethyl ketone, methylamylketone, mesityloxide and of sodium levulinate (CH3COCH2CHzCOONa) gavesomewhat less satisfactory brighteners.

Acetylacetone and acetol reacted very violently with sodium hydroxide(50%) and carbon disulfide, and' were thus not suitable as startingm'aterials. e

As far as the easeof obtaining these addition agents in solid form ofreproducible brightening efficiency and in reasonablygood yieldconcerned, I prefer the 'acetonylacetone-carbon disulfide reactionproducts as described in Examples 1 and 3'. a V

r I claim:

1. A process for producing bright silver electrodeposits, whichcomprises electrodepositing silver from an aqueous cyanide silverplating bath containing 0.02 to 0.04 oz./gal. (0.15 to 0.30 g./liter) ofthe solid, waterand acid insoluble but alkali soluble reaction productof a ketone of the formula RCHzCOCHs, where R comprises a substituentselected from the group consisting of hydrogen, alkyl, acetonyl(CH3COCH2--) and alkali metal carboxymethyl (-CH2COONa,= CH2COOK), withcarbon disulfide and alkali hydroxide, this reaction product having beenprecipitated by addition of a strong mineral acid and freed from alkalisulfide and hydrogen sulfide.

- 2.-A -process for producing bright silver elec trodeposits, whichcomprises electrodepositing silver from an aqueous cyanidesilver platingbath containing 0.4 to 1.6 m1./l.' of an aqueous solution of Turkey redoil, 50%, and 0.02 to 0.04 oz./gal; (0.15 to 0.30 g./liter) of thesolidywaterand acid insoluble but alkali soluble reaction product of aketone of the formula RCHzCOCHs, where R comprises a substituentselected from the group consisting of hydrogen, alkyl, acetonyl(CH3COCH2) V and alkali metal carb'oxymethyl CH2CO ONa,

CH2COOK)', with carbon disulfide and alkali hydroxide, this reactionproduct having been precipitated by addition of a strong minera1 acidand freed from alkali sulfide and hydrogen sulfide.

3. A process for producing bright silver'elecf trodeposits, whichcomprises Lelectrodepositing silver from an aqueous cyanide silverplating bath containing 0.02 to 0.04 ozL/gal. (0.15 to 0.30 g./liter) ofthe solid, waterand acid insoluble but alkali soluble reaction productof a ketone of the formula RCH2COCH3, where R comprises a substituentselected from the group consisting of hydrogen, alkyl, acetonyl(CH3COCH2) and alkali metal carboxymethyl (CH2COONa, CH2COOK) awithsubstantially two mols carbondisumde per mol carbonyl group and at1east=oneand-a half mols alkali hydroxideper mol carbon disulfide, thisreaction product having :been precipitated by addition ofa. strongmineral acid and freed from alkali sulfide and hydrogen sulfide.

" ILJA process for producing bright-silver electrod'ep'osits, whichcomprises electrodepositing silver from an aqueous cyanide silverplating bath cbntainingmi. to '1' .6 'mL/i. of an aqueous Solution ofTurkey red'oil, 50%, and 0.02 to 10.04 on/gal. (0.15 to.'0.'30"g:/liter)' or the solid, waterand acid insoluble but alkalisoluble reactionxproductof a keton'e'ofthe fori'nula RCHiCOCHa, where Rcomprises a substituent seiect'ed'irom the group consisting oflhydrogemalkyl, acetonyl- (CHYCO C H tone, methyl ethyl ketone andacetone, wi=th-carbon disulztide' and alkalihydroxide, this reactionproduct having beenprecipitated by addition-oi arcade/so 8. A processfor producing bright silver electrodeposits, which compriseselectrodepositing silver from an aqueous cyanide.-- silver plating bathcontaining 0.4 to 1.6 m1 .71. of an aqueous solutionof Turkey red oil,50%, and 0.02 to 0.04 oz./gal. (0.15 to 0.30 g./liter) of the solid,waterand acid insoluble" but alkali s'oluble reaction product of aketone, selected from 'a group 'oonsisting of 'acetonyl aeetone, methylethyl=ketone and acetone, with '-substantially Ltwo rnols-carbondisulfide' p'er inol carbonyl group and at=least one'and-a half molsalkali hydroxide per mol carbon disulfide; this reaction product: havingbeen precipitated by addition of a strong mineral acid and freed fromalkali sulfide and hydrogen sulfide. l

"9. A process for producing bright silver electrodeposits; which(rim-prises "electrodepositing si-l'ver f-roman aqueous 'cyanide silverplating bath containing 0". 02 to 0.'04"oz./gal; '('0.15'*to-0.30

g./liter) of the solid, waterand acid insoluble but alkali solublereaction product of a ketone, selected from a group consisting ofacetonylacetone, methyl ethyl ketone and acetonewith substantially twomols carbon disul-fide per-incl carbonyl group and at least one-andahalf mols alkali hydroxide, in the form of a concentrated aqueoussolution, per mol carbon disulfid'e. this 1 reaction having been allowedto proceed-between astrons mineral acid and freed from alkali su-lmic ndhydrog n ulfide 6, A proc ess for producing bright silverelectrodeposits, which comprises electrodepositing silver. irom :anaqueous cyanide silver; plating bath containing 0.4 to 1.6 n l/l. of anaqueous solution (of, Turkey red oil, 50%, and "0.012 to 0.04 oz ./gal.(0.15 -to.0.30 g ./liter) of the solid, waterand acid insoluble butalkali soluble reaction product of a ketone, selected from. a :gmupconsistingiof acetonylacetone, methyl; ethyl .ketone and acetone, withcarbon disu-l fide and alkalivhy di xide, t is r act n product havi beenpro.

cipitated by addition 0f a strong; ,minera-l; acid and freed fromalkalisulfide and hydrogensultide. 1 l 1 1. A proces .i p ducin bri ht si verelectrodeposits, which comprises electrodepofiting .and acid insolublebut alkali soluble reaction product of a ketone, selected from agroup-consisting of acetonylacetone, methyl ethyl ketone and acetonewith substantially two mols carbon disulfide per mol carbonyl group andat least one and a half mols alkali hydroxide, in the form of, a-.concentrated' aqueous solution, per mol' carbon disulfide, thisreaction having been allowed to proceed between 30 and 50 G.-at leastuntil the initially heterogeneous reaction mixture became homogeneousand this reaction product having been precipitated by addition of astrong mineral acid and freed from alkali sulfide and hydrogen sulfide;

OTTO KARDOS.

References Cited in the file of'this patent UNITED STATES PATENTS NumberName Date 2,110,792 "Egberg et al. Mar. 8, 1938 2,113,517 Powell et a1.Apr. '5, 1938 2,176,668 Egbert; et 3.1. Oct. 1'7, 1939 OTHER REFERENCESSer. No. 351,241, Weiner (A. P. 0.), published May '18. 1943'. 1

1. A PROCESS FOR PRODUCING BRIGHT SILVER ELECTRODEPOSITS, WHICHCOMPRISES ELECTRODEPOSITING SILVER FROM AN AQUEOUS CYANIDE SILVERPLATING BATH CONTAINING 0.02 TO 0.04 OZ./GAL. (0.15 TO 0.30 G./LITER) OFTHE SOLID, WATER- AND ACID INSOLUBLE BUT ALKALI SOLUBLE REACTION PRODUCTOF A KETONE OF THE FORMULA RC2COCH3, WHERE R COMPRISES A SUBSTITUENTSELECTED FROM THE GROUP CONSISTING OF HYDROGEN, ALKYL, ACETONYL(CH3COCH2-) AND ALKALI METAL CARBOXYMETHYL (-CH2COONA, -CH2COOK), WITHCARBON DISULFIDE AND ALKALI HYDROXIDE, THIS REACTION PRODUCT HAVING BEENPRECIPITATED BY ADDITION OF A STRONG MINERAL ACID AND FREED FROM ALKALISULFIDE AND HYDROGEN SULFIDE